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Thread: How to change tire size on LL8?

  1. #21
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    Hmmm interesting...
    I think I may know a shop in a neighboring town with a Tech 2. I can check tomorrow. Is there an OS version you'd recommend that you think would fix my problem or is that just opening up doors to more trouble with other things?

    Thanks Erik. I appreciate all the help you've given me.

    - b

  2. #22
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    I havent had any greater success with different P10 OSs, its the way the speedo calculator works on the P10s thats the problem.

    Anyone know the formula to hand calc the values for these tables?

    Just curious, what OS are you running now? Im using 12575262, its the 2nd to last 2002 OS IIRC.
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, tuned, turbo mods, etc.
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

  3. #23
    Lifetime Member Chevy366's Avatar
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    Go here and enter VIN info http://tis2web.xw.gm.com/tis2web , at least you can find out latest OS for your TB and what updates or fixes if anything .
    Last edited by Chevy366; August 5th, 2009 at 02:08 PM.
    2005 1500 HD , Custom OS3 SD tune .
    2006 Trailblazer
    Dinosaurs and Plants gave their lives so that we may drive , long live fossil fuel .

  4. #24
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    I'm running OS 12579357.

    Yeah, if anyone had any tips as to what values might affect the speedo readout at all, I could work on figuring out the equation, but so far I haven't been able to generate any change whatsoever with H0101, H0104, H0105, or B0205. I've given up on the speedo calc tool and was just entering in values manually. As I mentioned before H0101 does inversely affect the VSS reading though.

    I checked out the GM website... here's what I get:
    Calibration History for: Speedometer
    Part Number CVN Bulletin # Description
    12580498 00008583 - Part number change only, same as prior calibration
    12574176 00007291 - Speedometer calibration
    Any idea what this means?

  5. #25
    Lifetime Member Chevy366's Avatar
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    Quote Originally Posted by Whodunnit View Post
    I'm running OS 12579357.

    Yeah, if anyone had any tips as to what values might affect the speedo readout at all, I could work on figuring out the equation, but so far I haven't been able to generate any change whatsoever with H0101, H0104, H0105, or B0205. I've given up on the speedo calc tool and was just entering in values manually. As I mentioned before H0101 does inversely affect the VSS reading though.

    I checked out the GM website... here's what I get:
    Calibration History for: Speedometer
    Part Number CVN Bulletin # Description
    12580498 00008583 - Part number change only, same as prior calibration
    12574176 00007291 - Speedometer calibration
    Any idea what this means?
    After looking at the data again , the website will show if there is a updated cal for a specific area of the PCM , if there is a update it will show in a repository (registry) style tree , last being newer first being older , but any ways if you open your tune file EFILive will show cals listed for you OS .
    If OS number is different than yours it is newer , so you have to do a Tech II update to get that OS (sorry with P12 you can do a full falsh) .
    But does not mean it will calibrate tire size any better , but would be nice to see if it helped .
    Last edited by Chevy366; August 5th, 2009 at 03:22 PM.
    2005 1500 HD , Custom OS3 SD tune .
    2006 Trailblazer
    Dinosaurs and Plants gave their lives so that we may drive , long live fossil fuel .

  6. #26
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    Red face


    Oh!... thanks for your help. It's finally starting to make sense now... at least the OS revisions are.

    It looks like I'm up to date with the Speedo cals... but for the record here's what I have outstanding:
    Calibration History for: Operating system
    Part Number CVN Bulletin # Description
    12588012 00000D5E - New software to improve idle stability

    Calibration History for: Engine
    Part Number CVN Bulletin # Description
    12591968 00001D2F - New calibration with diagnostic enhancements for DTC P0130 and P0506. Also improvements to fuel trim and EVAP diagnostics.
    12588569 000059A8 - New calibration to improve idle stability
    12582726 0000AE66 - New calibration to correct problem occuring at the assembly plant. Does not address any service issues.

    Calibration History for: Transmission
    Part Number CVN Bulletin # Description
    12588580 00000B26 - New calibration to correct cold start/shift problems
    12583073 0000652D - New calibration to improve transmission shift quality

    Calibration History for: System
    Part Number CVN Bulletin # Description
    12588589 00005A32 - Enhanced Calibration for Cooling Fan Noise Reduction
    12581579 0000D550 - New calibration for improved fan control


  7. #27
    Lifetime Member Chevy366's Avatar
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    Quote Originally Posted by Whodunnit View Post

    Oh!... thanks for your help. It's finally starting to make sense now... at least the OS revisions are.

    It looks like I'm up to date with the Speedo cals... but for the record here's what I have outstanding:
    Calibration History for: Operating system
    Part Number CVN Bulletin # Description
    12588012 00000D5E - New software to improve idle stability

    Calibration History for: Engine
    Part Number CVN Bulletin # Description
    12591968 00001D2F - New calibration with diagnostic enhancements for DTC P0130 and P0506. Also improvements to fuel trim and EVAP diagnostics.
    12588569 000059A8 - New calibration to improve idle stability
    12582726 0000AE66 - New calibration to correct problem occuring at the assembly plant. Does not address any service issues.

    Calibration History for: Transmission
    Part Number CVN Bulletin # Description
    12588580 00000B26 - New calibration to correct cold start/shift problems
    12583073 0000652D - New calibration to improve transmission shift quality

    Calibration History for: System
    Part Number CVN Bulletin # Description
    12588589 00005A32 - Enhanced Calibration for Cooling Fan Noise Reduction
    12581579 0000D550 - New calibration for improved fan control

    Looks like there are a couple of updates for your PCM cals , sorry I have not messed with the Speedo Calculator on a P10 , so can't help you there .
    2005 1500 HD , Custom OS3 SD tune .
    2006 Trailblazer
    Dinosaurs and Plants gave their lives so that we may drive , long live fossil fuel .

  8. #28
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    Well I found a shop about 30minutes away that said they can do OS updates, but when asked if he had a Tech2 he said, "well, we have scanners...we can do it." I'm not real convinced that's going to solve my problem with EFI Live settings not having any affect, especially since the updates don't seem to directly hit on Speedo control, so at the tune of $150... benefits might not outweigh the risks.


    Would anyone mind helping me approach this a different way? I was looking at tinkering with the rev limiters in park/neutral, but it seem whatever values I input, I still can only rev to about 2.2k in P/N, which is annoyingly gutless and low, and makes me suspect that something with the EFI Live - LL8 programming might be amiss across the whole OS.

    Has anyone happened to notice if B1201, B1207, or B1208 has a direct 1:1 or any affect on their P/N Rev limits? I set mine as high as 10000, 9500, and 9200 respectively, but still no change; no dice!

  9. #29
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    Quote Originally Posted by Whodunnit View Post
    My speedo and VSS values are both reading 5.4% low. Intuitively I attempted to lower:
    {H0101} "Vehicle Speed Sensor Pulses per Kilometer"
    {H0104} "Trans Output Shaft Revs/Kilometer"
    {B0205} "Vehicle Speed Sensor Pulses Per Mile On Data bus"
    each by 5.4%, but that didn't seem to work. I don't see the {B0201} ScarabEpic22 mentioned anywhere?...

    I tried changing just {H0101} and {B0205} a different time, but the adjustment didn't come out correct and the car just ran rough after coasting to a stop (hmm.... I'm wondering if H0104 needs to be linearly scaled with H0101 because the Description box states "It will normally be consistent with the equation: H0101=H0102*H0104.")

    Do anyone happen to know if these values tend to be linearly scaled through zero (in a y=mx format) or is there an offset perhaps (such as y=mx+b)?

    Any help will be GREATLY !
    Thanks in advance!

    - bret
    i seem to found the problem, this may not have to do with the version of the efilive BUT rather the error of efilive using kilometers rather than meters measurement under H0104 when using the speedo calculator.

    there was a reason gm, pcmforless and waitforme does not follow the speedo cal because it leaves speedo off balance. if you were to adjust the tires and gear ratio and click apply Ho104 would use the measurements under kilometers, which is a no no. But based on the stock, pcmforless, and waitforme's tune they use the meter measurement instead. Like this for example.

    Click image for larger version. 

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    try that and see how it works. mine seems to be fine since i havent gotten any speed camra tickets (knock on wood)...
    2002 4.2L I6 Trailblazer LTZ

  10. #30
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    After searching both the Trailvoy and this forum, I haven't found a good mathematical explaination for the numbers here. It also seems that some of the calculations for H0104 and B0205 shown on my readout from my TB are off just bit, which could be why when I had the stock tires my speedo was a little off from my GPS. So, I tried to understand from a math standpoint what was going on, starting with H0101, which you should be then able to calculate H0104 and in theory, B0205.

    Just some quick background info, my blazer is an 03 SWB, 4wd, 3.73 open diff and came with BFG Long Trail T/As from the factory.

    The factory readout for my blazer shows H0101 = 65199.

    Using the equation H0101 = P*D*1000000/(T*pi)

    Where P = 40 (which seems to make sense, 40 pulses per revolution of the output shaft)
    Where D = 3.73 (in my case, since it uses 3.73 gears)
    1000000 = the number of milimeters in a kilometer
    Where T = 727.656mm

    Before I start, let me explain "T", as one might quickly point out that a 245/70/16 tire, measures 29.5" in diameter. That may be true in theory, however, if you look at the BFG website for the LongTrail T/A, you'll see that it is 704 revolutions per mile, which I as I understand is a measured distance with a given load on the tire.

    So to find out "T",
    Divide 5280 feet per mile, by 704 revolutions per mile. That gives you 1 revolution is equal to 7.5 feet.
    5280/704 = 7.5

    7.5 feet, times 12 inches per foot, gives you 90 inches per revolution.
    7.5*12 = 90

    Take 90 inches, divide by pi, and you get 28.6479 inches in diameter
    90/3.1415926 = 28.6479

    Multiply 28.6479 inches by 25.4mm per inch, and you get 727.656399mm
    28.6479*25.4 = 727.656

    I included the math for anyone that would like to check and ensure it was done correctly.

    Now back to H0101
    40*3.73*1000000/(T*pi) = 65266

    I know, not quite the 65199 number, but close.
    Rewriting the equation and solving for "T", using H0101 = 65199, I ended up with T being equal to 28.6776".

    So, that is a difference of my calculated diameter of 28.6776" - 28.6479" (from above) = .0298" in diameter!
    It would be safe to assume a little bit of rounding was used when BFG arrived at the 704 revolutions/mile number.

    The reason for the math was to simply understand where the number of 65199 came from. And I figured that if I could indeed calculate it out, that I could then properly calculate H0104 and B0205.

    Based on my math above, it is my belief that H0104 in the table listed in EFILive should not be labeled as "Trans Output Shaft Revs/Kilometer", but as in "Trans Output Shaft Revs/Mile".

    My table shows H0104 = 2637.4

    Here is the math.

    If H0101 = H0102*H0104,
    then H0104 = H0101/H0102.

    But 65199/40 = 1629.975, not the 2637.4 value shown in my table for H0104.

    However, multiplying 1629.975 by 1.609344 (which is the number of kilometers in 1 mile) is equal to 2622.63. Hmm, so 2637 - 2622 = 15. This is a difference of 15 revolutions of the driveshaft in one mile, which is 600 pulses. 600 pulses in a mile seems like it would be a huge amount of error. We'll look at that issue in a moment.

    15 revolutions of the driveshaft, divided by the 3.73 gear ratio, is 4 revolutions of the rear wheel. With a roll out distance of 7.5 feet per revolution of the rear wheel, this is equal to 30 feet. (7.5*4) in 1 mile.

    So according to this, the percent error is 1/2%. I'm not going to show how to calculate percent error.

    B0205 should also be able to be calculated the same way.

    Taking the 65199 * 1.609344 = 104927, which should be a good value to use for the B0205. I believe that this math is what EFILive is using to calculate the numbers for what they call "TOS" for H0104 and B0205.

    NOTE: This is all assuming that the transmission is using a 40 tooth reluctor, which is an assumption. I have not been able to confirm this, thats just what comes up when I do a search for replacement reluctors for the 4l60e trans.

    Also note, to calculate the H0101 number, you need to start with the revolutions per mile from your tire manufacturer's website and calculate back the diameter.

    This math also explains what goldbergv95 was showing in his chart with the circled numbers. I believe he means miles, not meters, otherwise the numbers would not match up.

    If all of this has been explained before, sorry, I couldn't find it. Woohoo, post number 1 for me!

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